Fix mypy error

Author: sadra-barikbin

ignite/handlers/checkpoint.py

@@ -287,7 +287,7 @@ def __init__(
         filename_pattern: Optional[str] = None,
         include_self: bool = False,
         greater_or_equal: bool = False,
-        save_on_rank: Optional[int] = 0,
+        save_on_rank: int = 0,
     ):
 
         if not isinstance(to_save, collections.Mapping):
@@ -791,7 +791,7 @@ def __init__(
         atomic: bool = True,
         create_dir: bool = True,
         require_empty: bool = True,
-        save_on_rank: Optional[int] = 0,
+        save_on_rank: int = 0,
         **kwargs: Any,
     ):
         self.dirname = Path(dirname).expanduser()
@@ -957,7 +957,7 @@ def __init__(
         filename_pattern: Optional[str] = None,
         include_self: bool = False,
         greater_or_equal: bool = False,
-        save_on_rank: Optional[int] = 0,
+        save_on_rank: int = 0,
         **kwargs: Any,
     ):